Resistance unit



Aug. 1s', 1.925. 1,550,641

v G. H. WHITTINGHAM RESISTANCE UNIT Filed April 25, 1924 5 Sheets-Shoot '2 Aug.' 1s', 1925, 1,550,641

v G. H. wl-{ITTINGHAM 1 RES ISTANCE UNIT Filed April 25, 1924 3 Sheets-Sheet 3 l gwuwno'o,

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Patented Aug. 18, 1925| UNIT-ED STATES net.'

PATENr. oFFlc.

GEORGE H.

TROLLER COMPANY,

WHITTINGHAM, OF BALTIMORE, MARYLAND, ASSIGNOR TO MONITOR CON- OF BALTIMORE, MARYLAND, A CORPORATION OF MARYLAND.

RESISTANCE UNIT.

Application filed April 25, 1924. Serial: No. 708,943.

-posed of a relatively fiat bar of refractory material, preferably porcelain, and this is formed with screw threads in its edges.`

rlihe bar is preferably composed of relatively short sections, arranged end to end, the number of sections employed depending upon the desired length of the bar. These sections are held together and supported by metal strips arranged at opposite sides of the bar, each strip being secured to each section of the bar. The ends of the strips, at opposite ends of the bar, project beyond the ends of the latter, and they are off-set so as to lie in the centralplane of the bar and are suitably :Eormed for .connection to a supporting frame.

The resistance element comprises a helix formed lof a iat ribbon of resistance metal,

Y wound edgewise and iitting 'between the threads on the edges of the bar, the convolutions of the helix being spaced evenly apart by the threads. The internal diameter of the helix is such that its convolutions will freely iit between the threads in the edges of the bar, and the helix may be applied by threading it on to the bar. When the unit is in use, the bar extends horizontally and lies in a vertical plane, so that the air can flow upward on each side of the bar between the spaced convolutions of the resistance element, and these convolutions being of flat metal have large surfaces exposed'to the air so that the heat is quickly .carried 0E. Each helix or coil, like the Y bar, may be composed of short sections, so that a unit may be built up to any desired length. l

For use with alternating currents, the bar of refractory material is provided with double-screw threads on its edges, and two helices of resistance metal are threaded on to the bar, theses' helices being connected together at one end of the bar. e As the convolutions. of one helix alternates with the convolutions of the other, and the current flows in opposite directions through these convolutions, the induction between the helices is neutralized. -This prevents the generation of currents in the metal strips which supports the unit. Thes'e strips may, it desired, be riveted together through openings in the refractory material without becoming heated by induced currents.

In. the accompanying drawing,

Fig. 1 is a side elevation of a resistance unit embodying my improvements, the resistance element being sho-wn partly in section;

Fig. 2 is a top plan view of the same, the resistance element and supporting core being shown partly iny section;

Fig. 3 is a section on the line 3--3 'of Fig. 1, on a enlarged scale;

Fig. et is a side view of one of the supporting strips forming part of the core for supporting the resistance element;

Fig. 5 is asimilar view of the opposing strip;

Fig. 6 is a side elevation of a sectional bar of refractory material which carries the the line 10--10 of 11 is a side elevation of a resistance lunit in which the refractory bar is provided with double-screw threads on its edges and carries two coils which are connected together at one end of the unit to form a sin le resistance element; l

= ig. 12 is a top plan view of the same, the coils "being shown partly in section and the convolutions of one coil being shown in light lines to distinguish these convolutions from those of the other coil;

Fig. 13 is an end view of the unit shown in Fig. 11, looking from left to right; and, ligjll is a side elevation of a resistance co1 Referring to Figs. 1 to 7 inclusive, of the drawing, a represents a relatively fiat suprivets and an alternating current were V:ses

' sponding perforations sections of the porting core comp-rising a bar 1 of refractory material having on its edges screw threads 2, and this bar of refractory material is carried by metal supporting strips 3 and 4, secured to the sides of the bar. The bar 1 is preferably made of porcelain, molded in short sections 1, 1", and 1c, which are arranged end to end between the sup-porting strips and secured thereto. Each section of the bar is provided with rivet holes 5. The strip 3 is provided with perforations 6, adapted to aline with certain of the openings 5 Vin the refractory bar and with larger openings 7, arranged to register with otherI openings in said bar. Likewise the strip 4 is'provided with rivet holes 8, adapted to register with certain rivet holes in the bar and with alternate openings 9, larger than said rivet holes, adapted to register with other openings or perforations in the bar. The bar of refractory material is provided on each side with shoulders 10 and shallow channels 11 are thus formed in the side of the bar between the shoulders, for receiving the supporting strips. The supporting strips are provided with flanges 3a and 4, adapted to abut against the shoulders. In assembling the parts which form the core, rivets 12 are placed through the small perforations 6 in the bar 3 'and through rivet holes in the porcelain sections, and the ends of these rivets are turned over against the faces of these sections, as shown in Fig. 3. Similarly, rivets 13 arepassed through openings 8 in the strips 4 and through correin the porcelain members, vand are turned over against said members. The rivets which connect the strip 3 with the porcelain members project into the openings 9 in the strip 4, and the rivets which connect the strip 4 with the porcelain members project into the openings 7 in the b strip 3. These penings are larger than the over-turned ends of the rivets so that while the two strips/are connected to each of the refractory bar, and are connected together through the medium of said sections, theyL are not connected electrically by the rivets. This is to prevent local currents from circulating through the support-v ing strips, as would happen if the sup orting strips were electrically connecte by passed through the coil.

The end 4"I of the supporting strip 4 is o's'et and extends beyond one end of the core, and the end 3a of the supporting strip 3 is offset and projects beyond the opposite end of the core. These ends of the strips lie 1n they central plane of t-he refractory ban and they are suitably vformed at their ends for connection to a suitable supporting The resistanceelement b is composed of a flat ribbon of resistance metal wound edgea. plurality of wise into the form of al helix, the internal diameter of which is such that the convolutions of the helix will lie easily between the threads on the edges of the refractory bar, as shown in the drawing, and is applied by screwing it on to the bar. When in position, the convolutions of the helix are kept separate and spaced evenly apart by the teeth or threads on the bar. l/Vhen the unit is in use, the core is supported at its ends and is held in the horizontal position with the bar of refractory material lying in a vertical plane. As the ban is relatively flat and does not till the space within the coil, the air may pass freely through the spaces between the convolutions of the coil, at the sides of the bar, and as the coil is made from a flat ribbon a large area of the coil is exposed to the air which carries off the heat.

For convenience in connecting one unit to another, or to acurrent source, the. ends of the resistance element are extended upwardly, as shown in Fig. 3, and connectors c are provided for attachment to these projecting ends. As shown in Figs. 3 and 7, each connector is threaded at its ends to receive clamping nuts 14, and at the ends of the threaded portions are shoulders 15. Each end of the connector has a slot 16, adapted to receive one end of a resistance element, this slot extending to a distance beyondk the shoulder 15, which is somewhat less than the width of the end of the resistance element. Washers 17 are provided between'the nuts 14 and shoulders 15 and when the end of the resistance element is inserted in the inner part of the slot, the nut is tightened and this presses the walls of the slot against the sides of the ribbon composing the resistance element and the washer 17 bears against one edge of the ribbon and the latter ecomes clamped between the washer and the end of the slot. The connectors are provided with threaded openings .18 to receive binding screws by which wires may be connected to the elements.

In Fig. 8,'I have shown a series or bank of resistance units A, A, A2 and A3, connected in series by connector c, the same as shown in Fig. 7, and the ends of the units are shown'supported by rods 19.

Fig. 9 shows a heating element b2, composed of a series of short sections 20, 21, 22, 23, and 24, each section being connected at one end to the end of an adjoining section. The resistance element may be built u .to. any desired length by using a series of) short units and each point of connection between the sections provides a convenient 'place to connect lead wires, such as 25 and 26, to the element.

10, the ends of the nected by They may, however, be connected 1n various ways.

As shown in Figs. 9 and short sections are conscrews 27 andl clampin nuts 28.

In Figs. 11 and 12, the core for the heating element is the same as in the previously described figures except that the edges of the refractory bar` are provided with double' screw threads 2a and 2b, and two helices b and b2 are threaded on to the bar, the ends of these helices at one end of the bar being riveted or otherwise connected together, as shown at 29. Thus, the coils are connected in series with the convolutions of one coil alternating with the convolutions of the other coil, and it will be evident that when an alternating current is passed through the resistance element, the inductive eect between the coi-ls will be neutralized. Hence, the metal supporting strips 3 and 4 willbe .free from inducedcurrents and for that i reason, if desired, the rivets 30 may extend from one strip through the porcelain parts to the other strip, andvmay be headed over on the latter strip.

What I claim is: 1. A Iresistance unit comprising a relativel iat bar of refractory material having threads on its edges, metal supporting strips 4secured to the opposite sides ofthe bar, the

opposite ends o the strips extending from opposite ends of the bar, and a helix of flat resistance metal having its coils arranged 30 edgewise between the threads.

2. A resistance unit comprising a relatively flat bar of refractory material composed of several sections arranged end to end and i having threads on their edges, two 'metal supporting strips arranged on opposite sides ofv the bar, each strip being secured to each section andthe strips being insulated from one another, and a helix of iiat resistance metal having its coils arranged edgewise be-- tween the threads.

4. A resistance unit comprising a relatively flat bar of refractory materialhavin longitudinal channels on its sides am? threads on its edges, metal supporting strips fitting in said channels and a helix oi flatV resistance metal having its coils arranged edgewise between the threads.

f In testimony whereof I hereunto aix myV signature.

GEORGE H. WHITTINGHAM. 

